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181.
Evolution of antibiotic resistance genes: the DNA sequence of a kanamycin resistance gene from Staphylococcus aureus 总被引:14,自引:0,他引:14
The kanamycin resistance gene from Staphylococcus aureus has been sequenced
and its structure compared with similar genes isolated from Streptomyces
fradiae and from two transposons, Tn5 and Tn903, originally isolated from
Klebsiella pneumoniae and Salmonella typhimurium, respectively. The genes
are all homologous but, since their common ancestor, have undergone
extensive divergence, with more than 43% divergence between the closest
pair. The phylogeny of the genes cannot be made congruent to the phylogeny
of the taxa from which they were isolated without requiring rather
improbable differences in rates. One is therefore led to conclude that
there have been multiple occurrences of gene transfer between these
species. Thus, although they are homologous, they are neither orthologous
nor paralogous. It is suggested that homologous genes of this type be
called xenologous.
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184.
Olga V Savinova Fumihiro Sugiyama Janice E Martin Stanislav I Tomarev Beverly J Paigen Richard S Smith Simon WM John 《BMC genetics》2001,2(1):12-15
Background
Little is known about genetic factors affecting intraocular pressure (IOP) in mice and other mammals. The purpose of this study was to determine the IOPs of genetically distinct mouse strains, assess the effects of factors such as age, sex and time of day on IOP in specific strain backgrounds, and to assess the effects of specific candidate gene mutations on IOP. 相似文献185.
We examined annual variation in the timing of conception andparturition in the African buffalo (Syncerus caffer) and thesynchrony of birth timing with resource cues, using 8 yearsof monthly birth, rainfall, and vegetation data, measured asNormalized Difference Vegetation Index (NDVI). Monthly birthshad the strongest significant correlations with NDVI and rainfalllevels 12 and 13 months in the past, respectively. In addition,the synchrony of current year births corresponds most stronglyto the synchrony of the previous year's NDVI distribution. Becausethe gestation period of buffalo has been estimated to be around11 months, these findings suggest that improved protein levels,occurring approximately a month after the first green flushof the wet season, are either a trigger for conception or conceptionhas evolved to be synchronous with correlated environmentalcues that ensure females enter a period of peak body conditionaround the time of conception and/or parturition. With a gestationperiod of approximately 340 days, parturition occurs to takeadvantage of the period when forage has its highest proteincontent. A comparative analysis of gestation periods withinthe subfamily Bovinae indicates that African buffalo have aprotracted gestation for their body size, which we suggest isan adaptation to their seasonal environment. We also found thatinterannual variation in the birth distribution suggests a degreeof plasticity in the date of conception, and variation in thenumber of calves born each year suggest further synchrony ata timescale longer than a single year. 相似文献
186.
Seasonal variation in conception and various pregnancy outcomes 总被引:1,自引:0,他引:1
187.
One major parvalbumin each was isolated from the skeletal muscle of two
reptiles, a boa snake, Boa constrictor, and a map turtle, Graptemys
geographica, while two parvalbumins were isolated from an amphibian, the
salamander Amphiuma means. The amino acid sequences of all four
parvalbumins were determined from the sequences of their tryptic peptides,
which were ordered partially by homology to other parvalbumins.
Phylogenetic study of these and 16 other parvalbumin sequences revealed
that the turtle parvalbumin belongs to beta lineage, while the salamander
sequences belong, one each, to the alpha and beta lineages defined by
Goodman and Pechere (1977). Boa parvalbumin, however, while belonging to
the beta lineage, clusters within the fish in all reasonably parsimonious
trees. The most parsimonious trees show many parallel or back mutations in
the evolution of many parvalbumin residues, although the residues
responsible for Ca2+ binding are very well conserved. These most
parsimonious trees show an actinopterygian rather than a crossoptyrigian
origin of the tetrapods in both the alpha and beta groups. One of two
electric eel parvalbumins is evolving more than 10 times faster than its
paralogous partner, suggesting it may be on its way to becoming a
pseudogene. It is concluded that varying rates of amino acid replacement,
much homoplasy, considerable gene duplication, plus complicated lineages
make the set of parvalbumin sequences unsuitable for systematic study of
the origin of the tetrapods and other higher-taxa divergence, although it
may be suitable within a genus or family.
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